The present invention relates to an optical transmission system suitable for transmitting frequency division multiplexed analog television signals over a single mode optical fiber. The invention is particularly suitable for CATV and television retransmission applications.
Optical fibers permit transmission of signals either in analog or digital form. Although suitable for long distance transmission, digital systems are costly and require a wide per-channel bandwidth. To avoid these disadvantages, attention has been focused on analog optical transmission systems using a laser diode to take advantage of its linearity and wide frequency range. Since the optical energy is a laser beam, single mode optical fiber can be advantageously employed. However, the laser diode is affected by optical energy that returns from the distant end of the optical fiber, resulting in reflection noise. There is also a signal distortion as a result of multiple reflections that occur between opposite ends of the transmission medium. While frequency modulation techniques may be used to avoid these problems, the maximum number of channels available for transmitting FM television signals is severely limited, typically to four channels.